Increased length of active labor is associated with adverse perinatal outcomes among nulliparous women undergoing labor induction.

Objective: Evaluate the association between current recommendations for active labor duration in nulliparous women undergoing labor induction and adverse perinatal outcomes.

Study Design: Retrospective cohort study from 2012 to 2015. Subjects were nulliparous, 18-44 years, cephalic, singleton ≥37 weeks undergoing labor induction who reached active labor. We created three subgroups, defined by active labor duration from 6 to 10cm as < the median, median-95th percentile, and >95th percentile based on contemporary labor curves. We evaluated the association between subgroups and cesarean delivery, chorioamnionitis, blood loss (EBL), 5-minute Apgar score < 7, and neonatal intensive care unit (NICU) admission using logistic regression.

Results: Among 356 women, 34.8% had an active labor duration < median, 43.3% were between the median-95th percentile, and 21.9% were >95th percentile. The risk of cesarean delivery increased with longer active labor duration; 1.8-fold (95%CI = 1.1-3.1) and 4.0-fold (95%CI = 2.5-6.5) for women whose active labors were between the median-95th percentile and >95th percentile, respectively. Chorioamnionitis increased by 3.9-fold (95%CI = 1.2-13.2) in the >95th percentile subgroup. Active labor length was not associated with EBL, Apgar scores, or NICU admission.

Conclusions: Cesarean delivery and chorioamnionitis increased significantly as induced active labor duration exceeded the median. This study provides a better understanding regarding the risks of longer active labor as defined by contemporary labor curves.